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Should a line from the COA bisect the w/b foot?

 
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PostPosted: Sat Nov 08, 2014 1:38 pm    Post subject: Should a line from the COA bisect the w/b foot?  Reply with quote

Does a line dropped from the centre of articulation bisect the weight bearing surface of the foot (from breakover to heel), or should there be more foot in front of this line?  

Is is possible to have any rule, or is every horse different?

How much do pathologies e.g. underrun heels, high palmar angles affect this?  And how much radiograph technique and foot position when the radiograph is taken?

How much are claims that there should be more foot in front of the COA based on poorly trimmed feet with long toes and high heels?

Is COA or COR the correct term for the point in the centre of a circle drawn in the bottom of P2?
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PostPosted: Sat Nov 08, 2014 1:54 pm    Post subject: Reply with quote

Suggestions that there should/may be more than half the weight bearing surface of the foot in front of the COA.

http://www.forgemagazine.co.uk/site/index-1newsarchiveapr09.html

The research did not support the common belief that the centre of rotation equally bisects the ground bearing surface.  The centre of rotation splits the trimmed ground bearing surface of the foot 60:40 dorso/palmar.
Surprisingly, the centre of rotation bisected the ground-bearing surface of all the feet in a near 60:40 split regardless of hoof shape or conformation. This is in marked contrast to claims made in many books and articles on farriery (Williams and Deacon, 1999), which states the centre of rotation of the coffin joint should bisect equally the ground-bearing surface of the foot. Our findings did, however, concur with a recent study (Craig and Craig 2005) in not supporting this 50:50 split. Their study found an average of 67.06 per cent of the ground bearing surface in front of the centre of rotation but had a higher standard deviation of 5.41 per cent (our study found 0.96 per cent). Although their study was based on radiographic evidence and not external reference points, they did not state what foot trimming protocol was used and so foot trimming may account for this variable.
The only way a bare foot horse may naturally have a centre of rotation 50:50 split in ground bearing surface may be when it has a broken forwards hoof pastern axis, which is a conformational trait,

References
CALDWELL, M. (2006)
CRAIG, J. J. & CRAIG, M. F. (2005) Hoof and Bone Morphology of the Equine Digit: American Farrier’s Journal.
DUCKETT. D (1990) The assessment of Hoof Symmetry and Applied Practical Shoeing by Use of an External Reference Point. International Farriery and Lameness Seminar. Newmarket, England. Second supplement,
p 1-11.
OVNICEK, G. D. (1997) New Hope for Soundness. EDSS Publishers.
RUSSELL, W. (1908) Scientific Horseshoeing. Robert Clark Company, Cincinnati Ohio.
SAVOLDI, M.T & ROSENBERG, G. F. (2003) www.americanfarriers.org
WILLIAMS DEACON (1999) In No Foot, No Horse, figure 3.1
P. Conroy (2008 submitted)
C. D’Arcy (2008 submitted)
P. Balchin & D. Mitchel (2008 submitted)
A. Shuttleworth & D. Beardmore (2008 submitted)
M. Oliver & M. Jones (2008 written up Foot Trimming Protocol submitted)
NB an external "centre of rotation" was used.
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PostPosted: Sat Nov 08, 2014 3:59 pm    Post subject: Reply with quote

file:///C:/Users/Andrea/Downloads/RotationCenters.pdf
Locating Rotation Centers of the Equine Digit and their Use in
Quantifying Conformation
John J. Craig, Phd ; Monique F. Craig, BSCE; Michael T. Savoldi; and James K. Waldsmith, D.V.M

This paper defines the COA as the point in the centre of a circle drawn in the bottom of P2.

"A central method used in our analysis of the latero-medial radiograph is the fitting of a circle to the distal ends of the first two phalanges, P1 and P2, and taking the center of those circles to represent the center of articulation (COA) of the corresponding joint."

"The range of motion experienced by the three joints in our experiment was approximately: 50 degrees for the coffin joint, 7 degrees for the pastern joint, and 60 degrees for the fetlock joint."

The study looked at the position of the COA of the coffin-joint
with regard to the support length of the foot, by dropping a perpendicular line down from the coffin joint's COA and looking at the distance from that line to the toe as a % of the distance from the toe to the (weight bearing) heel.  Looking at 131 feet, the average was that the toe to the COA was 67% of the total length of the (weight bearing) foot, with no feet with 50% or less in front of the COA.

However, the example x-ray shown (66.37% of the foot in front of the COA) has a breakover way in front of a line projected down the dorsal surface of P3, and there is a significant distance between the heels and the heel bulbs.  So is it the case that research is looking at less than perfect feet and considering this normal?

HOOF AND BONE MORPHOLOGY OF THE EQUINE DIGIT:
CHALLENGES TO SOME COMMON BELIEFS
John J. Craig, Phd, and Monique F. Craig, BSCE
160 front hooves - foot measured from back of heel points (paper suggests that frog may extend back from the heels, but this wasn't measured - so possibly not a true measure of the weight bearing surface of the foot) - an average of 53% of the foot was ahead of the widest part of the foot.

This research suggested that the COA is an average of 14% further back than the WPOTF.
This is interesting when compared to Gene Ovnicek's research, who found that with a palmar angle of >5 degrees, the WPOTF was behind the COA, otherwise it was in front - he concluded that the palmar angle affects the position of the WPOFT in relation to the COA.  The palmar angle isn't mentioned in the Craig research.  
http://www.lamenessprevention.org...ch&catid=27:pi&Itemid=120


Last edited by The Laminitis Site on Sat Nov 08, 2014 6:47 pm; edited 1 time in total
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PostPosted: Sat Nov 08, 2014 6:01 pm    Post subject: Reply with quote

Suggestions that the COA should be in the centre of the foot:

http://www.roodandriddle.com/hoofcapsuledistortion.html
Hoof Capsule Distortion And Its Relationship To Foot Lameness
Scott Morrison DVM
Scott Morrison says "Ideally the coffin joint should be in the center of the foot’s weight bearing surface".  Low heels/long toe will place the coffin joint further towards the back of the foot, increasing strain on the DDFT and likely creating a toe first landing.  Trimming and shoeing to maintain the COA of the coffin joint in the centre of the foot's weight bearing surface will help.

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